The Problem :

Switch Mode Power Supplies (SMPS) are widely used in electronics projects, but maintaining stable output voltage can be tricky. The feedback loop is critical—it regulates voltage by comparing the output to a reference and adjusting accordingly. If not designed properly, it can lead to voltage fluctuations, inefficiency, or even circuit failure.

The Solution :

Most SMPS designs use an optocoupler and a voltage reference IC (like TL431) to regulate output voltage. The key is choosing the right resistor divider network to set the feedback voltage correctly. Incorrect values can cause overvoltage or undervoltage issues.

Simple Fix: Adjust the resistor values to set the reference voltage accurately. Use a trimpot for fine-tuning if necessary.

Practical Example :

Imagine designing a 12V DC power supply for an Arduino project. The SMPS circuit includes a TL431 feedback IC. The reference voltage for TL431 is 2.5V, meaning you need to calculate the resistor divider to achieve this.

Sample Calculation :

Using the formula:

Vout = Vref × (1 + R1/R2)

For Vout = 12V and Vref = 2.5V, selecting R1 = 10kΩ, solving for R2:

R2 = (Vref × R1) / (Vout – Vref) = (2.5 × 10k) / (12 – 2.5) = 3.33kΩ

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